Notes From The Field

Uninvited Visitor on the Farallones

Pete Warzybok

Notes from the Field

Whether outwitting a predatory jay (to find a Blue-gray Gnatcatcher's nest) or praising a Mexican trogon (while teaching avian monitoring), field work is a PRBO hallmark. Presented here are just four of the many tales that far-flung PRBO biologists will tell from this year's field season.

Beep, beep, beep! Where am I? Wind blowing, gulls screaming: Yes! another day on the Farallones. I throw on a sweatshirt, jacket, hat, and gloves (standard summer attire on the island) and head to the murre blind. Here I sit for three to four hours each day observing a colony of Common Murres and adding to what is already one of the most comprehensive, long-term studies of seabirds in the world, with data dating back to 1971, several years before my birth.

Long-term research helps us understand the marine ecosystem of which the Farallones are a part. For example, we have learned that the murres' success from year to year (their ability to raise a chick and the over-winter survival of adults) is closely tied to the ocean's productivity. Monitoring the birds' success and examining what prey species they are bringing in to feed their chicks provides us with a good indication of how the whole system is functioning. With more than 30 years of observations on Farallon murres, we can see how the system has changed through time.

The murres in this colony are unusually noisy this morning, and as I open the window, I see many of them taking flight. Much to my surprise, and undoubtedly that of the murres, a juvenile California sea lion is galumphing through the plot! Sea lions commonly haul out around the island, often in large numbers, but it is very rare for one to be up this high where the murres breed. The startled murres take off, exposing and scattering their eggs, and Western Gulls are more than happy to have them for breakfast. The sea lion is probably also here looking for something to eat: it appears emaciated and weak but, apparently not recognizing the eggs as food, leaves them alone. Nonetheless, the damage is done. In a murre colony, where the birds lay their eggs on bare rock, many eggs and young chicks are lost without the adults there to protect them.

In good years, murres are capable of laying a replacement egg, and this is shaping up to be another good year- the fifth in a row, an extraordinary streak. Populations of most of the breeding species on Southeast Farallon have been increasing as more young survive and recruit into the colony. This is particularly noticeable for the murres. Last season we counted over 100,000 murres breeding on the island, the highest number recorded since PRBO began monitoring them and almost twice the number observed just four years ago. A few more years of favorable ocean conditions, coupled with high productivity and survival, could result in exponential growth for the murre population, perhaps approaching a return to historical numbers, when there were estimates of up to one million murres on the Farallones.

Unfortunately, natural disturbances, such as the appearance of a predator, an unusual storm event, or a misbehaving sea lion, can throw a kink in the works. This story was originally to have had a happy ending, in which good conditions persisted and all the murres that lost eggs laid again and later fledged chicks. The murres did indeed lay new eggs, and those that managed to keep their eggs are now caring for young chicks. But shortly before this article was due, the sea lion returned, and this time it not only flushed birds but also, apparently finding the chicks more palatable than the eggs, began feeding. It has returned several times since and caused the loss of more than 30 chicks and 40 eggs. There is nothing we can do but observe and record these events as they happen. The disturbance caused by the sea lion will hurt productivity this season but ultimately be but a blip in the long-term data. The murres will rebound next season, and the population will continue to grow as long as favorable conditions persist.

I already can't wait until next year.

As each year builds upon another, environmental scientists relish the prospect of seeing something new and compelling. While no two years are ever the same, there is constancy in a long-term study--repeating the same methods at the same site to ensure comparability. Yet remarkable things do happen, as witnessed in this report from Southeast Farallon Island. The story of a fluke disruption is told against the backdrop of major positive change in the fundamental oceanic process, upwelling, that supports the Gulf of the Farallones food web. We have witnessed enormous productivity in the ocean surrounding the Farallones for four years in a row (possibly five, depending on how this year turns out), unprecedented in our 33-year history, and the seabird populations are growing as a result. Even so, for the Common Murres of one Farallon colony, 2003 will be always be "the year of the sea lion."

William J. Sydeman, PhD, Director, Marine Ecology Division

Pete Warzybok is a Marine Ecology Division staff biologist now in his third full season studying seabirds at our Farallon Island Field Station.